A lab method in which diluted oil flows across a glass slide over a strong magnet, which lays ferrous particles out in rows by size while nonferrous debris settles between them. An analyst studies the slide, called a ferrogram, under a bichromatic microscope and classifies particles by shape, color and size: rubbing platelets, cutting chips, fatigue chunks, spheres, red and dark oxides and copper alloys. It tells you the wear mode, not just the amount.
Analytical ferrography shows fatigue chunks and dark oxides, that bearing is spalling, not just running dirty.
It is skilled, slow and costly, so most programs run it only when a screening result such as PQ or particle count trips an alarm.
Also heard as
- ferrography
- ferrogram
- AF
- wear particle analysis
Related terms
PQ index
Magnetic measure of total ferrous debris in an oil sample, including large particles that spectrometers miss.
Elemental analysis
Spectrometric measurement of wear metals, contaminants and additive elements in oil, in parts per million.
Spalling
Flaking of large chunks from a bearing race or gear tooth after fatigue cracks below the surface link up.
Oil analysis
Lab testing of in-service oil samples to judge oil condition, contamination and machine wear.